How to prevent double from rounding up to two decimal

Question

I'm trying to calculate a percentage(9% tax) of a item

double amount = 55.4;
double total = amount * 0.09;

System.out.printf ("%f \n", total);
System.out.printf ("%.2f \n", total);

Returns

4.986000

4.99

How do I make it return 4.98?

Thanks!

`System.out.printf("%.2f%n", Math.floor(total * 100) / 100.0);` — Elliott Frisch, Jan 10 '20 at 11:59
Wow, why does it work? And is there a way to change it at the variable level instead of the print level? — Michelle C, Jan 10 '20 at 12:04
Take a look to this https://stackoverflow.com/a/12684082/4210091 — Renato, Jan 10 '20 at 12:09

score 2 · Answer 1 · answered Jan 10 '20 at 12:21

2

Use BigDecimal instead of double.

double is floating point, which cannot accurately represent all fractional amounts, hence the "rounding" problem that you are.experiencing.

BigDecimal is arbitrary-precision, and so doesn't have that problem.

answered Jan 10 '20 at 12:21

GreyBeardedGeek

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score 0 · Answer 2 · answered Jan 10 '20 at 12:13

If you want to chop off the thousands place multiple your total by 100 and cast it to an int, then divide it by 100 and cast it to a double:

double amount = 55.4;
double total = amount * 0.09;
int truncated = (int) (total * 100);
double val = truncated * .01;

System.out.printf("%.2f\n", val);

This will give you: 4.98

This can also be done with

double val = Math.floor(total * 100) / 100;
System.out.printf("%.2f\n", val);

How to prevent double from rounding up to two decimal

2 Answers2